This invention relates to a door closing device for reinforcing a closing force when a door is closed.
Recently, there has appeared a type of door closing device in which a door closer main body is fixed to a vertical portion of a door frame and in which a guide rail is fixed to an upper portion of the door. The door closing device restricts the opening movement of the door when opened and exerts a closing or latching force on the door when the door is released. A slide member is slidably held by the guide rail and urged by a tension spring in the direction where the door is closed. The slide member is rotatably connected to the door closer main body through a connecting arm.
In this type of the door closing device there is minimal space for mounting the door closer main body on the vertical frame. Accordingly, as only a small door closer main body can be used, sufficient door closing force cannot be obtained to maintain a latching force when the door is completely closed. To compensate for the lack of the latching force, the tension spring is generally provided along the guide rail.
The tension spring is expanded or compressed through a total stroke of the door opening and closing movements. Therefore, the tension spring is expanded for a relatively long distance. This requires a substantially large spring to assure durability. Further, the reliability of the door closing device is decreased. In addition, the size of the guide rail must be increased.